This invention relates to hot melt adhesives, and particularly to hot melt adhesives which are compostable or biodegradeable and which are based on specific thermoplastic polymers containing at least one hydroxy group per repeat unit.
Hot melt adhesives are used commercially for a wide variety of applications. The major advantage of hot melt adhesive systems is the lack of a carrier fluid which eliminates the need for drying the adhesive film once it is applied to the substrate. This elimination of the drying step overcomes hazards associated with solvent usage and also allows for faster production line speeds and lower transportation costs. Depending on the desired use, the degree of tack of the hot melt adhesives may be varied over a wide range to produce adhesives varying from pressure sensitive to non-pressure sensitive in character. Non-pressure sensitives are used, for example, in bookbinding, bag ending, case and carton sealing. Pressure sensitive hot melts are used in many applications, and particularly in disposables such as diapers, sanitary products and the like, where room temperature tack and long open time are often required.
Hot melt adhesives have historically been based on petroleum derived polymers such as polyethylene, ethylene-vinyl acetate, styrenic block copolymers, and polypropylene to name a few. These compositions are further tackified, plasticized, and reinforced with a variety of resins, oils and waxes which are derived from both petroleum and naturally occurring feedstocks such as wood, gum and tall oil rosin and terpenes. These classic compositions are generally very resistant to degradation once the articles employing them are disposed of.
The present invention stems from the growing movement to utilize raw materials which have demonstrated some level of degradation. Such compositions advance the state of the art of hot melt adhesives by allowing for the development of hot melt adhesives which either degrade naturally after coming in contact with the soil or which can be composted.
It has been suggested to use various biodegradeable polymers such as hydroxybutyrate/hydroxyvalerates and polylactide homo- or copolymers as the base polymers in hot melt adhesives; however, these prior biodegradeable adhesives suffer with respect to their mechanical and thermal stability when compared with other conventional hot melt adhesives.